1. Field of the Invention
The present invention relates to a controller for an air conditioner, and more particularly to a controller for an air conditioner, which has a cooling mode for effecting a cooling operation and a heating mode for effecting a heating operation and which automatically changes an operation mode of an air conditioner so that room temperature becomes a predetermined set value.
2. Description of the Related Art
As a prior art on which the present invention is based, there exists Japanese Patent Application Laid-Open No. 63-217159. This technique disclosed therein compares the temperature of a room to be air-conditioned (i.e., room temperature) and a predetermined set temperature with each other and effects on-off control of an air conditioner so that the room temperature becomes the predetermined set temperature. Further, a temperature region including the set temperature in the center thereof is previously determined as an observing region. When an operation mode is a heating mode and the period of time in which the room temperature resides in a first region which exceeds an upper limit of the observing region is greater than or equal to a predetermined value, the operation mode is changed from a heating mode to a cooling mode. When the operation mode is the cooling mode and the period of time in which the room temperature resides in a second region which is less than a lower limit of the observing region is greater than or equal to the predetermined value, the operation mode is changed from the cooling mode to the heating mode. With this technique, when load within the room to be air-conditioned temporarily varies, for example, when a door opens and closes, or when the number of indoor users increases or decreases, the operation mode is adapted to not change within the predetermined observing region so as to not unnecessarily change in accordance with variations in the temperature within the room.
However, in the above-described prior art, the operation mode is to be changed without considering a tendency of temperature variation when the period of time in which the room temperature resides within the first region is longer than or equal to the predetermined value. Accordingly, even if, during operation in the heating mode, the room temperature near the upper limit of the observing region has a tendency to fall, the operation mode is changed to the cooling mode. For this reason, even when it is predicted that the room temperature will become a value within the observing region without changing the operation mode, the operation mode is changed and a compressor is actuated, so that the room temperature is forcibly controlled to be the set value. Accordingly, there was a drawback in that the air-conditioning cannot be controlled so that the users feel comfortable.
Further, when the period of time in which the room temperature resides within the second region is longer than or equal to the predetermined time, i.e., even when, during operation in the cooling mode, the room temperature near the lower limit of the observing region has a tendency to rise and it is predicted that the room temperature will become a value within the observing region, the operation mode is changed to the heating mode. Accordingly, there also existed the drawback as described above.